This section of this document introduces information about and/or from the art that may provide context for or be related to the subject matter described herein and/or claimed below. It provides background information to facilitate a better understanding of various aspects of the present invention. This is a discussion of “related” art. That such art is related in no way implies that it is also “prior” art. The related art may or may not be prior art. The discussion in this section of this document is to be read in this light, and not as admissions of prior art.
Diphenylphosphinobutane (“DPB”) is a flexible diphosphine ligand with a bite angle of 97°. DIOP, 2,3-O-isopropylidene-2,3-dihydroxy-1,4-bis[bis(3,5-di-n-alkylphenyl)phosphino]butane (“Ligand A1”) and trans-1,2-bis[bis(3,5-di-n-alkylphenyl)phosphino]-cyclobutane (“Ligand B2”) are constrained diphosphine ligands with bite angles of between 100°-110°. DIOP, Ligand A1 and Ligand B2 have four carbons between the two phosphine moieties and will form a seven membered ring when coordinated to Rhodium (“Rh”). Such a catalyst system with Ligand A1 is disclosed and claimed in U.S. Pat. No. 7,271,295, incorporated by reference below. A catalyst system employing Ligand B2 is disclosed and claimed in U.S. Pat. No. 7,294,602, also incorporated by reference below.
The process of producing 4-hydroxybutyraldehyde (“HBA”) comprises reacting allyl alcohol (“AA”) with a CO/H2 mixture in the presence of a catalyst, typically a Rh complex with phosphine ligands. The initial products are HBA and lesser value products such as 3-hydroxy-2-methylpionaldehyde (“HMPA”) and byproducts such as n-propanol, (“n-Pr”) and propionaldehyde, (“PA”). The hydroxyl aldehydes are hydrogenated to give the final corresponding diols, Butanediol (“BDO”) and 2-Methylpropane diol (“MPDiol”).
While catalyst systems can employ both mono- and bidentate phosphine ligands, the latter have been the focus of research because they have shown marked improvements in the yield to HBA over HMPA coupled with the reduction of process losses to the byproducts n-Pr and PA. Progression in improvements from the catalyst system consisting of the monodentate, triphenylphosphine, (“TPP”) as the main ligand to systems containing, bidentate phosphines such as DIOP and 2,3-O-isopropylidene-2,3-dihydroxy-1,4-bis[bis(3,5-di-n-alkylphenyl)phosphino]butane, (Ligand A1), U.S. Pat. No. 7,271,295 have been achieved. One ligand in these series, trans-1,2-bis[bis(3,5-di-n-alkylphenyl)phosphino]-cyclobutane, (“Ligand B2”), as disclosed in U.S. Pat. No. 7,294,602, has been shown on batch scale to give improved results, 20% reduction in MPDiol in favor of BDO, compared to Ligand A1 while maintaining low n-Pr make and preserving rate. This disclosure serves to reveal more advantages of the Ligand B2 system observed under continuous pilot run conditions.
Several hydroformylation processes for diphosphines are available to the art, all of which are competent for their intended purposes. The art however is always receptive to improvements or alternative means, methods and configurations. Therefore the art will well receive the technique described herein.